Attenuation of regional seismic phases (Lg and Sn) in Eastern Mongolia

We present tomographic models of frequency-dependent Lg and Sn attenuation in eastern Mongolia using data from 228 local earthquakes that were recorded by 69 broad-band seismic stations. We adopt the two-station method (TSM) and reverse two-station method (RTM) to measure the frequency-dependent Sn and Lg Q values, respectively. The RTM has the advantage of allowing us to make attenuation measurements that are independent of site effects, instrument responses and source parameters. We have tomographically mapped Lg Q and η in order to understand spatial variations in crustal attenuation across eastern Mongolia and the surrounding regions. High Lg attenuation and low η are found in the volcanic region of the Middle Gobi Desert, while high Lg attenuation and high η are found in and around the tectonically active regions of the South Gobi Desert. We have also examined uppermost mantle attenuation by mapping the variation in Sn attenuation and η values. Regions of high Sn attenuation are found in the mountainous and volcanically active regions of the Middle Gobi Desert. Our Lg and Sn attenuation models correlate well with lateral variations in velocity as well as with the major tectonic units that make up eastern Mongolia. High attenuation regions seem to be associated with lowvelocities, Quaternary volcanoes and Cenozoic tectonic activity.